where L is a lower triangular matrix. Note
that mod.NoiseVariance = Λ.
The model can also be described with unit variance, using a normalized
noise source v:

y=Gu+HLvcov(v)=I

mod1 = noisecnv(mod) converts the
model to a representation of the system [GH]
with nu+ny inputs
and ny outputs. All inputs are treated as measured,
and mod1 does not have any noise model. The former
noise input channels have names e@yname, where yname is
the name of the corresponding output.

mod2 = noisecnv(mod,'norm') converts
the model to a representation of the system [GHL]
with nu+ny inputs
and ny outputs. All inputs are treated as measured,
and mod2 does not have any noise model. The former
noise input channels have names v@yname, where yname is
the name of the corresponding output. Note that the noise variance
matrix factor L typically is uncertain (has a
nonzero covariance). This is taken into account in the uncertainty
description of mod2.

If mod is a time series, that is, nu =
0, mod1 is a model that describes the
transfer function H with measured input channels.
Analogously, mod2 describes the transfer function HL.

Note the difference with subreferencing:

mod('m') gives a description of
G only.

mod(:,[]) gives a description of
the noise model characteristics as a time-series model, that is, it
describes H and also the covariance of e.
In contrast, noisecnv(m(:,[])) or noise2meas(m) describe
just the transfer function H. To obtain a description
of the normalized transfer function HL, use noisecnv(m(:,[]),'normalize') or noise2meas('normalize').

Converting the noise channels to measured inputs is useful to
study the properties of the individual transfer functions from noise
to output. It is also useful for transforming identified linear models
to representations that do not handle disturbance descriptions explicitly.

Examples

Identify a model with a measured component (G)
and a non-trivial noise component (H). Compare
the amplitude of the measured component's frequency response to the
noise component's spectrum amplitude. You must convert the noise
component into a measured one by using noisecnv if
you want to compare its behavior against a truly measured component.